I am reviewing the HMC856 eval board schematic on page 12 of the HMC856 data sheet. I am trying to figure out how to interface the control (B0-B4) to LVTTL (1.8, 2.5 or 3.3V) control system. Is it possible?
HMC856
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The HMC856 is a wideband time delay device with a 5-bit
digital control designed for timing compensation or clock skew
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Datasheet
HMC856 on Analog.com
I am reviewing the HMC856 eval board schematic on page 12 of the HMC856 data sheet. I am trying to figure out how to interface the control (B0-B4) to LVTTL (1.8, 2.5 or 3.3V) control system. Is it possible?
Hi,
One way to do is connect positive ports B0-B4 to a fixed voltage with a resistance, say 1.2k to GND and connect transistor switches to negative ports(B0~B4) with 2.7kohms each. Transistor switches can either be open or short to Vee. This way (B0-B4) change state. LVTTLs can drive switch transistors.
If you supply shift the part between 3.3V and GND, and if LVTTLs can supply enough current, you wouldnt need interfacing transistors/level shifters. The RF signal though should be AC couple in that case.
Sinan
Hi,
I saw the HMC856 Eval board schematic (page 12 of the datasheet) and the B0-B4 ports are connected differently.
The positive ports B0-B4 are connected singularly to a test point with a 2.7KOhm resistor while the negative ports B0-B4 are connected together with 1.2KOhm to a test point. Your suggestion is not applicable to HMC856 Eval board. Is it correct?
Could you help me to understand the right way to management the B0-B4 ports of the HMC856 Eval board?
Could you help me to understand the right way to management the B0-B4 ports of the HMC856 with LVTTL signals?
Best Regards,
Daniele
Control pins have internal 600ohms and there is a voltage division with externally connected resistors which are pulled down to -3.3V.
Hi,
in the eval board, the 600 Ohm internal pull ups are connected to VT. The VT-J8 pin is floating (I didn't see a specific interconnection) while you supposed that this pin is connected to GND. It is correct?
Best Regards,
Daniele
VT should be tied to GND, you are correct.